1. Field of the Invention
The present invention relates to an optical device used in an optical apparatus making use of polarization, and an optical head apparatus for reproducing the information signal of an optical recording medium.
2. Related Art of the Invention
The optical head apparatus used in an optical information processing apparatus for recording and reproducing information on an in optomagnetic disk medium is required to have a focus detecting function for forming a tiny spot on an optical disk, or a track detecting function for tracing a desired track accurately. The optical head apparatus is further demanded to have a function for detecting rotation in the direction of polarization by the optomagnetic recording disk medium.
A conventional optical head apparatus was disclosed, for example, in the Japanese Laid-Open Patent No. 3-29137. FIG. 16 is a structural diagram of a conventional optical head apparatus. Referring to this diagram, a conventional optical head apparatus is described below. The light emitted from a semiconductor laser 101 is transformed into parallel light by a collimating lens 102, and is condensed on an optical disk 105 by an objective lens 103 through a beam splitter 106 and a total reflection prism 110. The reflected light from the optical disk 105 is transformed again into parallel light by the objective lens 103, and is put into the beam splitter 106 through the total reflection prism 110, and is reflected by the beam splitter 106. The light reflected by the beam splitter 106 is transformed into a focusing light by a detector lens 104, and is put into a polarizing and separating hologram 120 made of lithium niobate. The z-axis of this crystal is disposed so as to have an inclination of 45 degrees to a principal direction of polarization of incident light. The polarizing and separating hologram 120 separates the polarized component in the z-axis direction of crystal and its orthogonal polarized light component into transmitted light and diffracted light. The negative primary diffracted light from the polarizing and separating hologram 120 is received by a photo detector 193, and positive primary light by a photo detector 194, and the transmitted light is received by a photo detector 192, and from the difference between the sum of the outputs of the photo detector 193 and photo detector 194, and the output of the photo detector 192, a recorded and reproduced signal can be obtained.
FIG. 17 is a diagram for showing the configuration of lattice pattern of polarizing and separating hologram 120 and segment division pattern of photo detector 194. In order to detect focus error and tracking error by using the positive primary diffracted light, the polarizing and separating hologram 120 is divided into four regions, and the photo detector 194 is divided into six segments. In a first lattice pattern area 181, while a light spot is formed correctly on the optical disk 105, the lattice is formed so that the incident light into this region may be focused at point A of the photo detector 194. Similarly, a second lattice pattern area 182, a third lattice pattern area 183, and a fourth lattice pattern area 184 form lattices so that the incident light of each region may be focused at point B, point C, and point D of the photo detector 194, respectively. A focus error signal is obtained from the differential signal of the sum of S1 and S4 and the sum of S2 and S3, and a tracking error signal is obtained from the differential signal of S5 and S6.
In the conventional optical head apparatus, the focus error signal and tracking error signal were detected by one polarization only. Therefore, six head amplifiers were needed to detect the signal. Furthermore, the optomagnetic signal for detecting by the operation of diffracted light and non-diffracted light caused deterioration because of the extreme imbalance of one head amplifier at the non-diffracted light side and five amplifiers at the diffracted light side.
Moreover, in the optical head of disk system or the like for employing the three-beam method for detection of tracking error signal and reading wobbling information of grooves by the push-pull method, the spot was complicated and it was hard to realize.
It is hence a primary object of the invention to present an optical head apparatus and optical device capable of decreasing the number of head amplifiers for detection of a signal, and eliminating imbalance of head amplifiers of optomagnetic signals.